Electrical connectors are used to form electrical connections between circuit boards that each contains a high density of electrical contacts. The contacts are arranged in a series of rows and columns in a contact field on one side of the circuit board. The contacts are closely spaced and a large number of contacts are included in a relatively small area.
One type of high-density electrical connector includes a flexible circuit having a contact field located on one side of the flexible circuit. The contact field includes contacts for electrically interconnecting the flexible circuit with another contact field. The flexible circuit is mounted on a backing member or clamp member on the opposite side of the flexible circuit across from the contacts. The clamp member carries a spring that faces the flexible circuit.
The clamp member is held against the circuit board with the contacts of the flexible circuit overlaying corresponding contacts of the circuit board. The spring is compressed between the support member and the circuit board, the spring generating a spring force pressing the contacts of the flexible circuit against the contacts of the circuit board.
The spring is formed as a compression mat or pressure pad made from an elastomeric material. Conventional compression mats have a number of holes or voids that extend at least partially through the mat and define a number of pillars or fingers spaced apart by the holes or voids. The pillars are arranged to overlay the contacts of the flexible circuit. Compressing the mat compresses the pillars, each pillar pressing a contact of the flexible circuit against the corresponding contact of the circuit board to electrically connect the two contacts.
The pillars are interconnected by elastomeric material adjacent to the side of the mat away from the flexible circuit. As the spring is compressed, the interconnecting material is also compressed and attempts to bulge or grow outwardly in a single common plane. Outward growth of the interconnecting material is resisted by the pillars on the outer perimeter of the compression mat, causing some or all of the outer pillars to buckle. The buckled pillars apply insufficient spring force to the contacts, and poor or no electrical connections are made between the contacts.
Increasing the strength of the pillars to resist buckling is ineffective. The size of the holes between pillars can be reduced to more closely space the pillars and increase the cross sectional area of each pillar. However, the pillars also bulge outwardly as the spring is compressed. If the pillars are too closely spaced together, the sides of adjacent pillars contact and interfere with each other as the spring is compressed. The interference prevents the pillars from applying sufficient spring force to the contacts, and poor or no electrical connections are made between the contacts.
As the number and density of electrical contacts increases, the size and spacing of the pillars decreases. This makes it more difficult to design a compression mat that can reliably apply a spring force to a large number of contacts without the pillars buckling or without the pillars interfering with one another. Thus there is a need for an improved electrical connector having a compression mat that can reliably apply a spring force to a large number of closely spaced electrical contacts while minimizing the tendency of the pillars to buckle or interfere with each another.